DISSERTATION RESEARCH:Sea level rise and vegetation regime shifts: implications for soil carbon storage and vulnerability in coastal wetlands

沿海湿地过滤水，缓冲海岸线免受风暴的影响，提供重要的栖息地，对全球碳储存具有重要意义。湿地土壤中的碳储量可能是长期的，并通过增加沉积物海拔的变化影响湿地在海平面上升期间是否会持续存在。气候变化和当地淡水管理增加了咸水向沿海淡水湿地的流动，改变了湿地的条件，并导致那里生长的植被类型发生变化。在许多热带和亚热带沿海湿地，红树林正在取代以草为主的沼泽，这对土壤储存碳的能力产生了不确定的影响。沿海湿地尤其如此，因为它们对海平面上升很敏感。本研究的目的是确定湿地土壤中碳储量的变化以及二氧化碳和甲烷气体释放到大气中的变化，这些变化发生在沿海湿地从以草为主的沼泽到红树林的变化过程中。研究结果将为佛罗里达大沼泽地的保护和恢复以及世界各地的沿海湿地提供有价值的信息。此外，这些发现将提供对不断变化的世界中植物与土壤相互作用和生态系统功能的更广泛理解。该项目将在佛罗里达国际大学的推广活动“沼泽管理大会”期间为当地高中生提供鉴定和种植湿地植物以及恢复城市沿海湿地的科学经验。这项活动还将为本科生提供在一个少数民族占多数的机构的实验室和实地经验。本研究将利用佛罗里达州那不勒斯万岛国家野生动物保护区的植被梯度，其中海平面上升和淡水操纵驱动植被变化和红树林侵占，以了解不断变化的非生物条件和植被状态变化如何随着时间的推移改变碳储量。变化的碳储量将被测量为当前的有机碳储量（地上和地下生物量、土壤碳含量）、输入（根系生产力、沉积物表面增加）和碳损失（有机碳分解率、气体通量测量）、过去的碳固存率（土壤放射性测年法）和潜在的未来碳损失率（有机质的相互移植，代表淡水恢复或持续的盐水入侵）。具体而言，本项目的目标是：1)确定以咸淡沼泽、咸水沼泽和红树林为主的植被群落在碳储存、增加和气体通量方面的差异。2)确定不同湿地类型土壤碳动态差异的非生物和生物机制。3)通过基于土壤测年和历史航空摄影建立红树林侵蚀时序，量化红树林建立以来对土壤碳储量、碳积累和气体通量的影响。

Coastal wetlands filter water, buffer the coastline from storms, provide important habitat and are globally important for the storage of carbon. Carbon storage in wetland soils can be for the long-term and influences whether wetlands will persist during sea level rise by increasing a change in sediment elevation. Climate change and local freshwater management are increasing the movement of saltwater into coastal freshwater wetlands, altering the conditions of the wetlands and causing shifts in the types of vegetation growing there. In many tropical and subtropical coastal wetlands, mangroves are replacing grass-dominated marshes, with uncertain effects on the capability of soils to store carbon. This is especially true of coastal wetlands, because of their sensitivity to sea level rise. The goals of this study are to identify changes in the storage of carbon in wetland soils and releases to the atmosphere of the gases carbon dioxide and methane that occur as coastal wetland change from marshes dominated by grasses to mangrove forests. The research findings will provide valuable information for the conservation and restoration of the Florida Everglades locally as well as coastal wetlands throughout the world. Furthermore, the findings will provide a broader understanding of plant and soil interactions and ecosystem function in a changing world. The project will provide hands on scientific experience identifying and growing wetland plants and restoring urban coastal wetlands for local high school students during "Marsh Mangress", an outreach activity at Florida International University. This activity will also provide undergraduate students with laboratory and field experience at a majority minority institution. This research will utilize a vegetation gradient in 10,000 Islands National Wildlife Refuge in Naples, FL in which sea level rise and freshwater manipulation have driven vegetation change and mangrove encroachment, in order to understand how changing abiotic conditions and vegetation state change alter carbon storage through time. Changing carbon storage will be measured as current organic carbon stocks (above and belowground biomass, soil carbon content), inputs (root productivity, sediment surface accretion) and carbon losses (breakdown rates of organic carbon, gas flux measurements), past carbon sequestration rate (radiometric soil dating), and potential future rates of carbon loss (reciprocal transplant of organic matter to represent freshwater restoration or continuing saltwater intrusion). Specifically, the goals of this project are to: 1) Identify differences in carbon storage, accretion, and gas flux among wetlands dominated by brackish marsh, saltwater marsh, and mangrove-dominated vegetation communities. 2) Determine which abiotic and biotic mechanisms drive differences in soil carbon dynamics among wetland types. 3) Quantify the effect of time since mangrove establishment on soil carbon storage, accretion and gas flux by establishing a chronosequence of mangrove encroachment based on soil dating and historic aerial photography.